Survival of Escherichia coli O157, Salmonella Enteritidis, Bacillus cereus and Clostridium botulinum in non-alcoholic beers

Why was the work done: To (i) determine whether microbial pathogens were present in packaged alcohol-free and low alcohol beers, (ii) to assess whether pathogens can survive or grow in non-alcoholic beers, and (iii) to determine the impact of pH and bitterness on their growth and survival of pathogens in alcohol-free beer. How was the work done: : 50 alcohol-free and low alcohol beers, available in the UK, were screened for pathogens and analysed for ABV, pH and bitterness (IBU). One of the alcohol-free beers (with the lowest IBU) was adjusted to 25 and 50 IBU and pH 3.8, 4.2, 4.6 and 4.9. Challenge testing of these beers was performed with Escherichia coli O157, Salmonella Enteritidis, Bacillus cereus and Clostridium botulinum. In addition, the heat resistance (D60 value) of the pathogens, spoilage bacteria and Saccharomyces cerevisiae ascospores in these beers was determined. What are the main findings: Salmonella, E. coli, Enterobacteriaceae, Bacillus cereus and sulphite reducing clostridia were not found in any of the 50 beers. However, two emerging opportunistic pathogens (Cupriavidus gilardii and Sphingomonas paucimobilis) were found in the low alcohol keg beers. None of the pathogens used in this study could grow in the alcohol-free beer at low pH (pH 3.8). E. coli O157 was unable to grow at pH 4.2 but could grow at pH 4.6 but only with reduced levels of carbon dioxide and increased oxygen. Salmonella Enteritidis was able to grow at pH 4.2 and 4.6 but also with reduced levels of CO2 and increased O2. Although Bacillus cereus and C. botulinum were unable to grow in any of the tested conditions, both pathogens were able to survive. Survival and/or growth of the microorganisms was impacted by pH; bitterness had no effect. Why is the work important: Salmonella Enteritidis and E. coli O157 only grew in alcohol free beer at a higher pH (4.2 and 4.6 for Salmonella and 4.6 for E. coli) together with with reduced levels of CO2 and increased O2. This suggests that packaged beer with appreciable levels of carbon dioxide and negligible levels of oxygen will not support the growth of pathogens. However, draught alcohol free beer may be vulnerable to pathogens.